This invention relates to a fuel injection valve for use in an internal combustion engine, which is adapted to vary the lift or lifting amount of the nozzle needle and accordingly the injection rate in response to operating parameters of the engine such as the rotational speed.
A conventional fuel injection valve for diesel engines or the like includes a nozzle needle and a nozzle spring for biasing the nozzle needle in the valve closing direction. The nozzle needle is lifted against the force of the nozzle spring by the pressure of pressurized fuel supplied from a fuel injection pump driven by the engine at speeds as a function of the rotational speed of the engine, to allow the fuel to be injected through the nozzle hole. The pressure of fuel pumped by the fuel injection pump increases at a rate substantially proportional to an increase in the rotational speed of the engine so that the lifting amount of the nozzle needle increases accordingly or at a rate substantially proportional to the increase of the engine speed, resulting in a corresponding increase in the injection rate. However, to achieve good operating characteristics of the engine, it is desirable that the injection rate of such a fuel injection valve should be controlled in response to operating conditions of the engine. Particularly in a low speed region of the engine, the injection rate should be reduced so as to make the operation of the engine stable in such low engine speed region, prevent idling noise of the engine, reduce the amount of hydrocarbons at low load operation of the engine, etc.
In attempt to comply with the above requirements, a fuel injection valve has been proposed by the assignee of the present application in Japanese Provisional Utility Model Publication No. 57-167257, which is capable of controlling the lifting amount of the nozzle needle in response to the rotational speed of the engine. According to this proposed fuel injection valve, a piston means is provided in a separate body from the main body of the fuel injection valve, which is displaceable in response to the rotational speed of the engine. A rod is connected to the piston means by means of a link mechanism and disposed in urging contact with a nozzle spring for axial displacement in the main body. Displacement of the piston means responsive to the rotational speed of the engine causes axial displacement of the rod through the link mechanism to thereby vary the set length of the nozzle spring and accordingly the lifting amount of the nozzle needle.
However, the proposed fuel injection valve inevitably has a complicated structure wherein the piston means is arranged outside the main body is connected to the latter through the link mechanism for controlling the valve. Further, the piston means is responsive to the rotational speed of the engine alone, but the provisional publication lacks any teaching of utilizing other operating parameters of the engine to control the valve.